The housing or the housing part typically comprises a porous body which serves as a flow-through device for providing a gas exchange connection between the interior of the housing and the surrounding area. This connection can serve the purpose of balancing the pressure difference between the interior of the housing and the surrounding area, which appears due to temperature changes, e.g. Additionally or in the alternative, the gas exchange connection through the gas-permeable porous body ensures that the pressure on the housing is limited in the event of an explosion, which takes place within the housing. The porous body thereby represents a gas-permeable barrier, which does not allow for flames and sparks or the like to escape out of the interior of the container to the outside. The porous body is thus embodied so as to be free from spark gaps and thus in a flameproof manner. Due to the fact that in the event of an explosion the gas volume can expand through the porous body to the outside into the surrounding area of the housing, the explosion pressure on the housing is limited so that the latter withstands the explosion and does not form any tears or gaps through which the flames or sparks could reach out of the interior of the housing to the outside
A housing part comprising a porous body for forming a pressure release device is known from U.S. Pat. No. 4,180,177 A. The porous body is inserted in a passage in the housing wall. To avoid water penetration into the housing, the porous body is covered by a flap. This flap opens, as soon as a sufficiently large overpressure appears in the interior of the housing. It is disadvantageous thereby that a certain overpressure must initially appear within the housing before the flap opens at all. Smaller pressure differences cannot be compensated continuously. The functional capability of the flap must be ensured and must be checked on a regular basis.
DE 10 2010 016 782 A1 describes a pressure release device comprising a nozzle having a passage in which a porous body is arranged. The passage in the nozzle can furthermore be covered completely by a membrane so as to prevent water from penetrating through the porous body into the housing. However, the membrane limits the volume or mass flow, respectively, through the porous body.
The use of an air-permeable membrane in the case of an air filter is proposed in EP 2 404 652 A1. However, the design described therein is not suitable for explosion-proof applications.
A ventilation and dewatering nozzle for a housing is known from DE 43 13 776 C1. A labyrinth arrangement, by means of which an air exchange is made possible, is present therein. Water can be discharged from the interior of the housing by means of the labyrinth arrangement, but the penetration of water into the interior of the housing is avoided.
U.S. Pat. No. 3,987,258 describes a splash water protective cover for a radio. However, an explosion protection is also not ensured.